Various types of liquid cleaning systems are used to clean printed circuit boards for removal of contaminates, such as flux residues, resins and the like, which remain on printed circuit boards emerging from the soldering process. Liquid cleaning systems, such as that disclosed in U.S. Pat. No. 5,113,882, incorporated herein by reference, typically include a series of processing chambers, each dedicated to a specific phase of the cleaning process, through which printed circuit boards pass. As shown in FIG. 1, printed circuit boards enter a liquid cleaning system on a conveyor chain or belt 10 and move through each cleaning chamber including a washing tank 22, hot water sprays 30, a second washing tank 32, and a drying chamber 38 from which printed circuit boards exit the cleaning system. Liquid cleaners used in such liquid cleaning systems include saponified cleaning agents and terpene-based solvents which have low flash points and are potentially flammable and explosive when sprayed in air. In addition, such liquid cleaning agents and solvents are highly volatile and produce unpleasant odors when released in air. For this reason, many liquid cleaning systems, such as shown in FIG. 1, are enclosed systems in which vapors and liquid particles produced from use of such cleaning agents and solvents are contained within the liquid cleaning systems by various means of condensation and air recirculation. Other liquid cleaning systems purge inert gas, such as N.sub.2, into the atmosphere of the cleaning chambers to displace air and minimize the potential for ignition or explosion, as well as to form liquid seals at the entrance and exit openings and between cleaning chambers.
Despite such methods, cleaning agent vapors are released into the air outside of the liquid cleaning system by evaporation of water particles and cleaning agent residues that are not removed in the drying chamber 38 and remain on printed circuit boards exiting the liquid cleaning system. The drying chamber 38 is typically the last phase of the cleaning process in which water particles and cleaning agent residues can be removed from clean printed circuit boards. It is, therefore, advantageous to substantially dry printed circuit boards within the liquid cleaning system before printed circuit boards are exposed to the external environment. It is also advantageous to remove cleaning agent residues from printed circuit boards as such residues can cause short circuits during performance tests of printed circuit boards and during the operation of printed circuit boards.
As shown in FIG. 1, prior art drying systems include the drying chamber 38 in which water and cleaning agent residues are removed from printed circuit boards by blowing steam and/or air onto the surfaces of printed surface boards. The drying chamber 38 is equipped with air diffusers 60 positioned above and below the conveyer belt 10 to provide a uniform flow of air onto both the top and bottom surfaces of the printed circuit boards. The dryer chamber 38 is also equipped with heaters 62 to warm air and deflectors 64 to direct air flow. Another embodiment of prior art dryers is shown in FIG. 2 and includes directional nozzle dryers 201 positioned above and below the conveyor belt 10. The nozzle dryers include flexible metal tubing 202, capable of adjustment to direct air flow, and nozzle heads of various designs, such as flare and fan nozzle heads 203. Other prior art drying systems utilize air knife dryers to deliver compressed air to the surfaces of printed circuit boards.
Prior art dryers such as those described above, are typically positioned above and below printed circuit boards as the circuit boards are conveyed through the drying chamber. Prior art dryers primarily function to dry only the top and bottom surfaces of printed circuit boards and are not capable of directing sufficient steam and/or air to remove water and cleaning agent residues from the sides of printed circuit boards nor any electrical components mounted thereon. Prior art drying systems typically used in liquid cleaning systems do not provide for side drying.
Prior art dryers use typically steam and/or normal, heated or pressurized air as drying agents to forcibly remove water and residual cleaning agents from printed circuit boards. Air knife dryers are used particularly to concentrate and deliver pressurized air onto the surfaces of printed circuit boards, forcibly removing remaining water particles and cleaning agent residues.